Never mind Eddie Mair’s evisceration of Boris Johnson. The Mayor’s circumlocutions aside, the fact that he is 5/1 favourite to succeed David Cameron says more about the Conservative Party than it does about his own feverish ambition.

The Tories’ woes have deepened since their disastrous Eastleigh by-election result. Last week’s Budget confirmed what we have long known: that their central gamble in 2010, on a quick return to growth in the time for 2015, has failed utterly.

At the last election, the economy was ticking along at an annualised growth rate of 2.8 per cent; the Office for Budget Responsibility now forecasts just 2.3 per cent in 2015. Why would the Tories win more seats with the economy in worse shape?

Labour are consistently 10 points ahead; frankly, they should be doing even better than that. But it would be enough to give them victory, as Lord Ashcroft’s huge poll in marginal constituencies earlier this month suggested: it gave Labour an 84-seat majority.

Just as ominous after Eastleigh, Ukip is polling the same or higher than the Lib-Dems — 12 per cent in yesterday’s YouGov poll, as opposed to 3.1 per cent in 2010. Ukip has made council by-election gains in recent weeks too.

Yet the response of Tory MPs is to talk to themselves. They need to win the Centre but they push Right. And if they’re not ranting about Europe — a subject that never polls in voters’ top 10 concerns, even as the eurozone crisis rages — they’re muttering about their next leader. According to Benedict Brogan’s devastating blog yesterday, many now see Cameron as a lame duck.

Which gives Johnson his chance. He could fudge the awkward timing of his mayoral term finishing in 2016: I expect him to pick up a safe seat in 2015 (Paddy Power is offering odds on which one) and fob Londoners off with the fiction that he can do both jobs for a year.

But as Johnson proved when he was an MP, he doesn’t have time for the hard graft or detail of the Commons. He is the opposite of a team player: he failed to build the alliances any leader needs, while proving an embarrassment even in the Westminster McJobs of shadow arts and higher education minister. And the sorts of failings that he manages to laugh off in City Hall, with its minimal media scrutiny and paucity of heavyweight opponents, would quickly ensnare him on the front benches.

In fairness, some Conservative MPs realise this. He can expect a vigorous “Stop Boris” campaign.

That will not prevent plenty of Tories backing his blond ambition: he is the darling of the party’s grassroots and media supporters. But if the Tories think Boris is the answer to their problems, they’re asking the wrong question.

A golden age of the Tube

The Tube’s iconography has become part of our mental map of the city, as shown by the London Transport Museum’s excellent Poster Art 150 exhibition (until October 27). Many images are familiar and the messages timeless — such as Fougasse’s 1944 cartoon urging passengers to move down inside the carriages.

But it’s noticeable how the show is dominated by striking posters from the Twenties and Thirties, a confident era on the network. In 1929, Charles Holden’s new 55 Broadway Tube headquarters was the capital’s tallest office building.

By contrast there are few posters from the Seventies and Eighties, the Tube’s nadir. It’s hard to know whether today’s bold 150th anniversary artwork will seem as familiar in 2105 as Charles Paine’s 1921 Regent’s Park penguins do today. But it’s still a welcome sign of a reinvigorated Tube network.

A new direction for the Bank?

One’s heart goes out to Diana Carney, wife of the incoming Bank of England Governor, Mark Carney. She tweets that finding a London home is hard, hamstrung as she is by the measly £250,000 taxpayer-funded housing subsidy her husband will receive for his new job on top of a £624,000 salary.

That sum might sound large compared with the $196,700 (£133,000) that US Federal Reserve chief Ben Bernanke gets but it is, for example, not vastly more than is trousered by some London council bosses (eg Paul Martin, Wandsworth: £254,880).

Happily, there’s a simple solution to the Canadians’ woes: go south. The new Governor could be at his desk within half an hour from Herne Hill; if he lived in Dulwich, it would be a longer walk but almost as safe as Ottawa. And he could afford to give us a chunky rebate. Now that’s my kind of quantitative easing.

You were just too nice, David

I’ve great respect for Peter Mandelson but he is surely unrealistic to hope there can be any way back for David Miliband, who is resigning as a Labour MP to work in the US. The elder Miliband brother was always the great Blairite hope, with good reason: not only was he politically moderate but he is articulate, bright and, well, a really nice guy.

And maybe that was part of the problem. When it came down to it, before Tony Blair’s departure in 2007 and from 2008, as Gordon Brown’s premiership unravelled, Miliband didn’t have the hunger or the brass neck to challenge Brown and his boot boys. By contrast, James Purnell resigned from the Cabinet in June 2009, telling Brown to go. His colleagues cowered — then lost. Perhaps successful politicians need to be lucky — but to make your own luck demands courage.